1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus equipped with the zoom lens, and more particularly, to a zoom lens suitable for a video camera, a digital camera, a monitoring camera, a silver-halide film camera, a broadcasting camera, and the like.
2. Description of the Related Art
In recent years, as an image pickup apparatus has been miniaturized with a high functionality, a photographic optical system used in the image pickup apparatus is required to have a zoom lens that is miniaturized in entirety and is capable of reducing a thickness of the camera with a high zoom ratio.
In order to implement a high zoom ratio and a miniaturized camera at the same time, there is known a retractable zoom lens, which can be stored in a camera casing when it is not used by reducing a distance between each lens unit up to a distance different from that of the imaging state. In addition, in order to reduce a thickness of the camera, there is known an optical-axis-bending zoom lens, in which a reflective member for bending an optical axis (optical path) of the photographic optical system by 90° such as a prism member using internal reflection is arranged in the middle of the optical path.
U.S. Pat. No. 7,982,970 discusses a four-unit zoom lens including first to fourth lens units of positive, negative, positive, and positive refractive powers, respectively, in order from an object side to an image side, in which an optical-axis-bending reflective member is arranged between the second and third lens units.
U.S. Pat. No. 7,889,436 discusses a five-unit zoom lens including first to fifth lens units of positive, negative, negative, positive, and positive refractive powers or positive, negative, negative, positive, and negative refractive powers in order from an object side to an image side, in which the optical-axis-bending reflective member is arranged between the second and third lens units.
In general, it is effective to increase the refractive powers (optical power=inverse of focal length) of each lens unit and reduce the number of lenses in the zoom lens to miniaturize the zoom lens. However, in such a zoom lens, as the refractive powers of each lens surface increase, the lens thickness increases in order to obtain an edge thickness. In particular, a front lens effective diameter (effective diameter of the first lens unit) increases, so that it is difficult to reduce the entire lens length. In addition, various types of aberration such as chromatic aberration increase at a telephoto end, and correction of such aberration is difficult.
In this regard, in order to implement a high zoom ratio and miniaturization of the entire zoom lens, it is important to appropriately set refractive powers, image-forming magnifications, and the like of each lens unit.
In a zoom lens having an optical-axis-bending reflective member between the lens units, a thin thickness of the camera can be easily obtained by arranging lens units in a thickness direction of the camera and a direction perpendicular thereto. However, it is important to appropriately set a configuration of the zoom lens to obtain such advantages. For example, it is important to appropriately set the arrangement of the reflective member in the middle of the optical path, movement amounts of each lens unit during zooming, and the like. In particular, if the refractive power of each lens unit, a movement amount of the zoom lens unit during zooming, and the like are not appropriate, various types of aberration increase significantly during zooming, and it is difficult to miniaturize the entire zoom lens with a high zoom ratio.